Mariah Carey was also seen in a debut video duet with Bieber, for her "All I Want for Christmas." The number resembled a big-budget department-store commercial, although the video's quick cuts made it difficult to determine whether the duo and their singers and dancers were actually in Macy's or Lord & Taylor.

Busta Rhymes joined Bieber for a rockin' rap version of "The Little Drummer Boy," while Usher and Bieber later performed the Nat "King" Cole standrad, "The Christmas Song (Chestnuts Roasting on an Open Fire)."

For good measure, the Radio City Music Hall Rockettes performed their signature, precision high steps.

Watching this all live in the plaza, where the outdoor temperatures were chilly: some 400,000 fans. By contrast, the tree itself, a majestic 74-ft. Norway spruce from Pennsylvania, only had 30,000 lights. Still, per tradition, it's a dazzler.